pod technicalities

[MICK H]

Hello all i am new to this forum and have been reading lots of threads on boat repairs, all very informative.What i would like to know is i'm going to put a pod on a 15 foot cruise craft rapide and run it with a 75 -85 hp motor, i understand that for every foot i go back i have to raise engine height 1 or 2 inches {please clarify}. my questions are 1. how long should i make the pod {450 mm -600 mm}
2,the pod is going to be extended from the hull ,at the back of the pod where the engine mounts, how high from the bottom of the pod should i mount the outboard , and 3. i'm going to make the pod myself from a mould of my own making, should i use marine ply inside the fibreglass for the engine mount or could it be made from core matt.?.aany help would be much appreciated.
forgot to mention i want to run a 25inch leg .
thanx....Mick

[MICK H]

This is the style of pod i'm going to build,

[jimbo59]

Gday mick ,i don't really like the look of the angle that the water takes on after coming out from under the hull in that photo,(to much dirty water)Another way is to box up the back of the transom and glass it straight to the bum,just continue the original shape of the hull and make it a 25mm longer than full tilt angle.

cheers...jim

[dnej]

I agree,go as an extension to the bottom.The pods can be bolted on, as they do with the VMR cats.Take a look at my pods.The transom is 25 inch,and the most important thing apparently,is the angle of the new stern, created by the pod.

Also, make sure you dont build in a banana shape, as this causes porpoising.My motor, sits the same height as normal.
David

[BM]

Mick,

One inch up for every 12 inches aft. This is the general rule of thumb.

1) Pod length is usally worked out on the basis of the engine being able to trim up fully. Typically 600mm will achieve this (probably even 550mm will do). This will of course be altered if you incorporate a mini splashwell in the transom.

2) Your engine mounting height will be determined by the height you set the pod at. EG: when I fit non full depth pods I set them as low as I can get them. This then requires an alloy plate (I use 25mm thick) which is sandwiched between the engine and the aft end of the pod.

3) Either marine, or structural ply (both have the waterproof glue and will be suitable) on the engine mounting face. I would not use core mat as I don't believe it has the strength.

Cheers

[Kerry]

BM, 25mm alloy plate ???? bit of an overkill isn't it, unless your hanging 1000hp off the thing??

[BM]

Sorry Big Kez

I should have said, if I am fitting a V6 to the pod I use a 25mm alloy plate. Smaller motors a 20mm plate will do (or less).

Cheers

[MICK H]

Thanks for your replies fellas and sorry i meant to say i'm going to make it an extension of the hull, idon't like the step up underneath either. I'm going to take a skin off the bottom of the boat at the back so i can get the exact shape. It will then bolt on from the inside of the pod and i will glass the boat to pod join for a perfect fit. It is mainly the dimensions i'm not exactly sure about and final hight of the motor mount .

[FNQCairns]

Mick the motor mount if you are doing a planing suface extension form of pod(good idea on your boat) can be viewed as simply the same mounting measurements as your current setup. With no lift (setback) nothing really changes (unless you want it to!.

cheers fnq

[MICK H]

Hi fnq is that the same if you use a longer leg eg: was 20 inch i want 25 inch leg. Should the transom or mount height be any different for a longer leg?

[BM]

You will need to lift the lip on your engine mount area by about 3 inches (if the present setup is to suit a standard 20inch long shaft) if you plan to fit a 25 inch engine. Otherwise you will not be able to raise the engine high enough to set your cav plate at the right height. By raising the upper edge of your mounting surface by 3 inches it gives you scope to play with (up and down) to get the perfect engine height.

Cheers

[MICK H]

Thanx BM ......cheers mate.

[SO70]

if you do your calculations right there is no need to mount the engine to an aluminium plate.
a full depth pod is virtually a hull extension which means more wetted surface area, more weight and more horsepower.
a non full depth pod means slightly higher engine mounting, propeller running in less turbulent water and less gearbox/skeg drag.

[FNQCairns]

25 inch leg, I am in the same boat, for eveything just add 5 inches and consider it the same, the extra height is nice to keep the powerhead away from the slop at the back.

cheers fnq

[Noelm]

a bit of confusion here, if the pod is just an extension of the bottom of the hull then the motor height does NOT change and the shaft length does not change the mounting height either (just the pod 'top" is 5 inches higher) the cav plate is still at the surface, BUT, if the pod is NOT an extension of the true bottom but has a large step up from the bottom, then the "up and back" comes into play, I posted a picture of this type of setup once before, so do not be confused, you van make an extension of the hull 10 feet long (I know you would not do so) and the motor height will still be the same.